The present disclosure relates to wind turbines, particularly shrouded wind turbines including at least one segmented shroud.
Conventional wind turbines have three blades and are oriented or pointed into the wind by computer controlled motors. These turbines typically require a supporting tower ranging from 60 to 90 meters in height. The blades generally rotate at a rotational speed of about 10 to 22 rpm. A gear box is commonly used to step up the speed to drive the generator, although some designs may directly drive an annular electric generator. Some turbines operate at a constant speed. However, more energy can be collected by using a variable speed turbine and a solid state power converter to interface the turbine with the generator. Such turbines are generally known as horizontal axis wind turbines, or HAWTs. Although HAWTs have achieved widespread usage, their efficiency is not optimized. In particular, they will not exceed the Betz limit of 59.3% efficiency in capturing the potential energy of the wind passing through it.
Several problems are associated with HAWTs in both construction and operation. The tall towers and long blades are difficult to transport. Massive tower construction is required to support the heavy blades, gearbox, and generator. Very tall and expensive cranes and skilled operators are needed for installation. In operation, HAWTs require an additional yaw control mechanism to turn the blades toward the wind. HAWTs typically have a high angle of attack on their airfoils that do not lend themselves to variable changes in wind flow. HAWTs are difficult to operate in near ground, turbulent winds. Ice build-up on the nacelle and the blades can cause power reduction and safety issues. Tall HAWTs may affect airport radar. Their height also makes them obtrusively visible across large areas, disrupting the appearance of the landscape and sometimes creating local opposition. Finally, downwind variants suffer from fatigue and structural failure caused by turbulence.
One type of wind turbine that has been developed to overcome the disadvantages of a HAWT is a shrouded wind turbine, such as that disclosed in U.S. patent application Ser. No. 12/054,050, which originally published on Sep. 25, 2008. The turbine has a turbine shroud composed of a ringed airfoil that is cambered to produce low pressure on the inside of the airfoil. The turbine may also have one or more ejector shrouds behind and partially enclosing the turbine shroud. The ejector shroud is also composed of a ringed airfoil that is cambered to produce low pressure on the inside of the airfoil. The shrouds may have mixing elements on their trailing edge. Energy is extracted using a prop or rotor/stator assembly with certain aerodynamic features that allow for improved power extraction from the wind energy. High-energy air is pumped into the wind turbine using the shrouds. The high-energy air mixes with and transfers energy to low-energy air downstream of the prop or rotor/stator assembly.
However, one disadvantage of this shrouded wind turbine is the extra cost of the materials needed to produce the increased power possible with this turbine. In addition, the increased surface area of the shrouded turbine increases the drag load experienced by the turbine from winds hitting it, particularly off-axis winds.
It would be desirable to provide a wind turbine design that could reduce the amount of materials used and reduce the drag load.